1. Field of the Invention
The present invention relates to a radio base station for carrying out radio communications with a plurality of radio terminals by adopting both a time division multiple access scheme and a space division multiple access scheme, and a frame configuration method for the radio base station.
2. Description of the Related Art
In recent years, demands for the radio data communications are increasing, and in conjunction with this, requests for allocating necessary radio bandwidths to respective radio terminals are also increasing. In order to make the radio bandwidths to be allocated to respective radio terminals variable, there is a need for a scheduler that makes radio bandwidth allocation adjustment among users. For example, a HIPERLAN2 proposed in the ESTI-BRAN (European Tele communications Standards Institute-Broadband Radio Access Networks) and a HiSWANa (High Speed Wireless Access Network a) proposed in the ARIB-MMAC (Association of Radio Industories and Businesses-Multimedia Mobile Access Communication systems) are radio systems of the centralized control type in which a MAC (Media Access Control) of the radio base station determines a frame configuration of each frame and broadcasts it to the radio terminal. For this reason, the HIPERLAN2 and HiSWANa are applicable not only to the radio LAN but also to a subscriber radio system called FWA (Fixed Wireless Access).
On the other hand, in order to utilize the limited radio frequencies effectively, a scheme called SDMA (Space Division Multiple Access) has been proposed recently. This is a scheme for suppressing interferences among radio terminals by controlling the antenna directivity. In this scheme, the radio base station is required to have one or more modulation/demodulation units in order to enable communications with different radio terminals at the same time using the same frequency.
However, up to now, there has been no proposition for a specific frame configuration method suitable for the case where a plurality of modulation/demodulation units are provided in a radio base station that carries out radio communications in the TDMA (Time Division Multiple Access) scheme using a frame configuration.